1. Field of the Invention
This invention relates, in general, to refrigeration apparatus for storing and transporting perishable commodities, and more particularly to portable, self-contained, refrigerated storage and transportation containers. Specifically, the invention relates to a refrigerated storage and transportation container having a closed liquid cooling system wherein the perishable commodities are bathed in the coolant to maintain them at a uniform cool temperature.
2. Description of the Prior Art
The use of individual, self-contained refrigerated containers for transporting fresh and frozen perishable commodities, such as meat, fish, poultry and produce, is well-known, and a variety of refrigeration systems and containers have been devised. One such system employs a closed refrigeration circuit in which a liquid refrigerant is circulated through coils or the like, and air is then blown across the cold coils. The cooled air is subsequently circulated throughout a container wherein the perishable commodities are stored. Examples of such systems are disclosed in U.S. Pat. Nos. 2,984,084, 3,175,606, 3,359,752, 3,699,870 and 3,733,849. One drawback of this type system is that a uniform cool temperature throughout the container is generally not obtained. This is caused by non-uniform circulation of the cool air through the container due to the presence of the commodities therein. Another drawback of this type system is that the refrigeration "cool down" capability of the container is relatively slow.
Another type of system for preserving perishable commodities while in transit utilizes cryogenic materials, such as liquid nitrogen, as the cooling source. Generally, the cryogen is stored as a liquid and then fed into the container wherein the perishable commodities are stored. Upon entry of the cryogen into the container, the liquid converts to a gas, and this gas is then circulated throughout the container. Examples of such systems are dsclosed in U.S. Pat. Nos. 3,421,336, 3,446,028 and 3,557,559. One problem with such systems is that the gas temperature frequently varies in different areas of the container, even if the same quantity of cryogen is introduced per unit length of the container. This may result in the thawing and re-freezing of delicate perishable commodities causing damage and loss. Finally, some cryogenic gases when improperly proportioned with oxygen have a deleterious effect on many kinds of fresh produce.
Yet another system utilized for storing and transporting perishable commodities incorporates both of the above-described systems. In such a system, a cryogen source cools incoming air which circulates throughout the storage container. In addition, at various interludes the cryogenic gas is leaked directly into the storage container. Such a system is disclosed in U.S. Pat. No. 3,385,073. While this system does overcome some of the above-noted problems, not all of them have been solved, and consequently spoilage of a certain portion of the perishable commodities is routine and expected during long transit and/or storage.
The present invention differs from the above-described systems in that the cooling source is a liquid and remains a liquid throughout the entire cooling process. Furthermore, this liquid coolant is sprayed directly onto the perishable commodities to maintain them at a uniform cool temperature, and the liquid coolant is itself cooled within the same chamber which contains the perishable commodities.